A. Field of the Invention
This invention pertains to devices for controlling the operation of pneumatic apparatus in a pneumatic control system. More particularly, this invention relates to a device of the type wherein the operation of the associated pneumatic apparatus is controlled by regulating the pressure in a pneumatic conduit, the conduit being connected to the pneumatic apparatus and to a pressure source. Most particularly, this invention relates to a device of the type wherein regulation of the pressure in the pneumatic conduit is accomplished by controlling the flow of air through a bleed orifice contained in the conduit.
B. Prior Art
Devices for providing pneumatic control of various apparatus are well known as typified by U.S. Pat. No. 3,233,105 (pneumatic controller) U.S. Pat. No. 3,613,951 (dispensing system), U.S. Pat. No. 3,680,739 (aerosol spray control) and U.S. Pat. Nos. 3,741,476 and 2,284,561 (thermostat controllers). Recently, there has been an increased demand for pneumatic control devices precipitated in large part by the desire on the part of many industries to switch over from electrical to pneumatic control systems. One reason for this change has been the increasingly complex electrical codes with which many electrical installations must comply. By switching to pneumatic control systems many of the increased costs occasioned by such compliance are avoided. Moreover, electrical control systems generally require more frequent and more complex maintenance than their pneumatic counterparts.
Generally, control systems serve to control the operation of various peripheral devices such as air-conditioners, boilers, lights etc. This function may be accomplished with pneumatic control systems by utilizing pneumatically activated switching.
In such systems, it is often desirable to provide some form of manual control for one or more of the peripheral devices, and accordingly, it is one object of this invention to provide a manually activatable timer controlled pneumatic control device wherein the period of activation is selectable at the outset of activation, the device having the capability of controlling the operation of one or more associated pneumatic apparatus, such as, for example, a pneumatically activated switch.